DES MOINES, Ia. -- New York Mayor Bill de Blasio flew the Democratic Party's liberal banner in Iowa Thursday to urge the critical presidential primary state to force the country to confront a "profound national crisis" of income inequality.

De Blasio said the growing divide between the rich and poor is "the profound challenge facing this country." He cited President Franklin D. Roosevelt and others who stemmed the divide in the 1920s, but said the problem is in ways worse now.

"The difference is that disparity is galloping forward," de Blasio said. "It is not being checked . . . today we are heading toward an iceberg and there is literally nothing emanating from Washington to change its course."

The speech at a progressive symposium at Drake University was de Blasio's second in two days to push presidential candidates, including Democrat Hillary Clinton, to confront the growing economic divide. He spoke in Nebraska Wednesday and is scheduled to speak in Wisconsin on April 25.

He has so far withheld his endorsement of Clinton until she articulates how she will confront this issue. De Blasio once worked in the Clinton White House and was Sen. Hillary Clinton's campaign manager.

"I have been beating this drum for quite a while with Team Clinton about the fact that these issues need to be addressed," he told reporters after the speech. He said he is optimistic she will.

De Blasio blamed everyone in power, including Democratic President Barack Obama, for failing to address the problem.

"I wish the president had early and often talked about income inequality and rallied the American people to address the issue, I wish that had happened earlier on in his administration," de Blasio said, while noting Obama made great strides in this area through his national health care initiative. But "first and foremost in my view the Congress has failed to act."

"He is clearly interested in becoming a national spokesman for the left of the Democratic Party," said political scientist Gerald Benjamin of the State University of New York at New Paltz. "Thus the measured -- even cool -- reaction to the Clinton announcement . . . ambition sunders ties of strange bed-fellows."

De Blasio outlined several measures to fix the problem, including encouraging more unionization by awarding more government contracts to unionized companies, raising the minimum wage to $15 an hour, free pre-kindergarten, and changing the tax structure so billionaires don't pay a smaller share of income taxes than the people who work for them.

"We have to be very clear we are going to reward work -- that's the underlying notion . . . not just people who are clever enough to take a lot of money and make a lot more money with it," he said in the speech.

"I'm not trying to punish success," he said. "I am trying to create more success stories."

Despite spending a day in the primary-powerful state, de Blasio insisted he has no plans to run for president in 2016 or 2020. "Let me say this into your phone," he told a reporter, "I have one ambition: I am running for re-election to mayor 2017."